In a conventional method for determining the direction to a laser beam source, use is made of a number of fixed receiver lobes facing in different directions. Since each receiver lobe is allocated a specific direction, an evaluation circuit can, on the basis of the light signal picked up by the respective receiver lobes, establish the direction to the laser beam source. A conventional method of this type is used, among other things, in so-called laser-warning systems and is known, for example, from DE Al 3,323,828. Laser-warning systems are mounted on tanks for example, with the purpose of warning the crew that they may be exposed to a threat. The threat can consist of a missile which is directed towards its target by a laser pointer. In order to be able to accurately determine the direction to the laser beam source, a large number of fixed receiver lobes with associated optics and detectors are required. Known laser-warning systems constructed in accordance with the conventional method with fixed receiver lobes are therefore both expensive and complicated.
The light from a laser beam source can be divided into three types of radiation, namely scattered, direct and reflected radiation. It is the scattered radiation which is of greatest interest for the present invention. The scattered radiation from a laser beam source with a narrow beam has a weakly decreasing amplitude with increasing distance from the laser within the area in question (for example 0.2 km to a distance which is less than the meteorological visibility prevailing at the time), when the measurement of the amplitude is carried out along a line which is parallel to the midline of the laser beam and when the angle of the receiver lobe to the laser lobe is constant. Also as regards this radiation, when the angle is constant, the power amplitude is halved when the perpendicular distance from the midline of the laser lobe to the receiver is doubled. Finally, the power amplitude is halved when the angle is doubled within the range from about 0.degree. to over 60.degree..